diff --git a/src/compat.h b/src/compat.h
index 79ebb932..70622169 100644
--- a/src/compat.h
+++ b/src/compat.h
@@ -11,6 +11,7 @@
 #ifndef NOMINMAX
 #define NOMINMAX
 #endif
+#define FD_SETSIZE 1024 // max number of fds in fd_set
 #include <winsock2.h>
 #include <mswsock.h>
 #include <ws2tcpip.h>